Laser bar code scanners employ a focused beam of light to repetitively scan across a bar code label. Typically, the scanning is produced by dynamic deflection of the source beam off of a rotating polygon reflector. Laser light reflections containing information from the scanned bar code are sensed in a photodetector. The bar code label encodes information as a series of bars of various widths formed on a contrasting background. The difference between the reflectance of the bars compared to the spaces produces a modulated optical signal. The detected optical signal representing reflections from the label is then converted into an electrical signal by the photodetector and that signal is further processed and then decoded.
A general and long known problem with laser bar code scanners is that the width of the scanning beam becomes narrower the closer the scanned object is to the scanner. The narrowing of the scanning area often requires that the item to be scanned be positioned carefully in a predetermined target area to ensure that the bar code is properly scanned.
One solution to reducing the above targeting constraint is to increase the distance between the object to be scanned and the scanner. This may not always be desirable. Also, there are circumstances in which close proximity between the scanner and the object to be scanned is essential. Another solution is to increase the optical path within the scanner so that the exiting scan beam is wider. While this method is effective, it usually requires increasing the dimensions of the scanning device which is usually undesirable, and can make the device entirely impractical for a number of applications.
One solution to the problem of widening the scanning area close to the scanner is to use a beam folding mirror to increase the optical path within the scanner housing, thereby increasing the scanning width, without commensurate increase in size of the scanner. However, while folding mirrors work quite well in other applications, including cameras and telescopes, mirrors introduce optical path distortion when used in conjunction with scanning reflectors (e.g. rotating polygon scan reflectors). One of the most serious problems is the generation of a curved scanning beam.
The curved scanning beam is commonly referred to as either a "sad" or "smile" face scan beam pattern. The "sad" or "smile" face scan pattern is generated by the distance translation of a rotating polygon reflector and a flat fold mirror about the polygon.
There is a need for a compact laser bar code scanner that produces a wide scanning area even when object to be scanned is placed close to the scanner. There is a further need that the beam have a flat, non-distorted scanning beam that can be produced by a compact laser bar code scanner that is reliable and economical to manufacture.